Field of the Invention
This invention relates to a shock absorber device intended to be placed between a suspended part which may, for example, be made up of the chassis or body of a vehicle and a non-suspended part which may, for example, consist of the wheels of a vehicle. More particularly, this invention relates to a shock absorber of the type shown in my copending application, Ser. No. 578,858, filed May 19, 1975, now U.S. Pat. No. 3,966,030, the disclosure of which is incorporated herein by reference and on which the present application is an improvement.
As stated in the above-mentioned copending application, the selection of the shock absorption value in a hydraulic shock absorber always involves a difficult compromise. It is in effect necessary to limit the shock absorption force during a compression movement of the absorber in such a fashion that an abrupt impact or shock, such as may result from the passage of a vehicle wheel over a bump in the road, will not cause an excessive acceleration of the entire suspended mass, while at the same time providing adequate absorption force for lesser impacts to provide a stable ride. This is accomplished in the shock absorber device disclosed in my above-mentioned patent application which makes it possible to absorb to the maximum extent the oscillations of the suspended mass during compression movements, while at the same time limiting the shock absorption force when the compression movement speed is great, that is to say, for example, when the vehicle wheel encounters a small-dimensioned obstacle which, however, causes an abrupt impact upon the shock absorber. In such a device, the absorption force decreases when the compression movement speed exceeds a predetermined limit value.
The shock absorber disclosed in my above-mentioned patent application is equipped with a control valve capable of establishing fluid communication between two chambers in a cylinder and separted by the main piston which is activated by a rod extending through one of the chambers. The control pressure of the control valve is obtained by restricting the flow to a reservoir of the fluid surplus resulting from the reduction in the useful volume of the cylinder following the penetration of the piston rod into the one cylinder chamber. The control valve can be a small ball or an equivalent element subject to the action of a movable element, such as an additional piston upon which acts a return spring.
When the speed of the rod, during a compression movement, exceeds a predetermined limit value, the differential pressure, acting upon the two faces of the moveable element, increases, and, beyond a predetermined limit value, causes the opening of the control valve which brings about a rapid reduction in the shock absorption force. The hydraulic pressure being exerted upon the movable element and causing the opening of the valve is a function of the displacement speed of the piston during a compression movement. Thus, there is produced an absorption force which is decreased as a function of the piston displacement speed.
In one embodiment described in my above-mentioned patent application, the piston is held by means of an elastic member whereby, when rod displacement speed is very great, the elastic member is initially compressed by the piston movement which brings about an increase in the volume of material submerged in the cylinder, thus bringing about the control of the valve as previously described before the shock absorption force has reached its maximum value.